1. Field of the Invention
The present invention relates generally to a spark ignition timing control system for an internal combustion engine, such as an automotive internal combustion engine. More specifically, the invention relates to a spark ignition timing control system for minimum advance for best torque (MBT) control.
2. Description of Background Art
In order to obtain optimum engine performance, it is essential to control a spark ignition timing appropriately. For this purpose, known MBT control is performed for obtaining maximum torque with minimum advance of spark advance angle for better fuel economy. In the known MBT control, FEEDBACK control is performed for reducing a difference between a timing where a maximum pressure in an engine cylinder is obtained and a preset target timing representative optimal timing to obtain better engine output. In such case, fluctuation of maximum pressure in the engine cylinder due to various unstable combustioning factors, tends to be fed back to cause fluctuation of the spark ignition timing to be derived based thereon. This tendency becomes higher when feedback loop gain is increased for improving response characteristics of spark ignition timing control.
In order to avoid such drawback, Japanese Patent First (unexamined) Publication (Tokkai) Showa 59-39974 proposes MBT control which utilizes an average value over a predetermined cycles of engine revolution as a timing of maximum pressure in the combustion chamber. Therefore, in the disclosed system, spark ignition timing is adjusted so that the timing to obtain the maximum pressure in the combustion chamber as represented by the average value toward the target timing. This system is successfully in providing stability in spark ignition timing control. However, on the other hand, this system clearly degrade response characteristics in transition.